Re: AWFUL reshape speed with raid5.

[Bill Davidsen <davidsen@tmr.com>]

Jon Nelson wrote:
> 1. metadata version matters. Why?
> 2. VERY LITTLE I/O takes place (between 0 and 100KB/s, typically no
> I/O at all) according to vmstat. Why? If it takes 1m34s to "grow" the
> array, but no I/O is taking place, then what is actually taking so
> long?
> 3. I removed the bitmap for these tests. Having a bitmap meant that
> the overall speed was REALLY HORRIBLE.
>
> The results:
>
> metadata: time taken
>
> 0.9: 27s
> 1.0: 27s
> 1.1: 37s
> 1.2: 1m34s
>
> Questions (repeated):
>
> 1. Why does the metadata version matter so much?
>   

I have no idea.

> 2. If no I/O is taking place, why does it take so long? [ NOTE: I/O
> must be taking place but why doesn't vmstat show it? ]
>   

vmstat doesn't tell you enough, you need a tool to show per-device and 
per-partition io, which will give you what you need. I can't put a 
finger on the one I wrote, but there are others.


-- 
Bill Davidsen <davidsen@tmr.com>
  "Woe unto the statesman who makes war without a reason that will still
  be valid when the war is over..." Otto von Bismark